Saint Mary's beacon. [volume] (Leonard Town, Md.) 1867-1983, 1887-02-03

phSboDeh Ia that bear upon the Ques-
ton OF the eafth's interior, namely,
the phenomena oEyoicanic action. The
study OF the meteriaIs elected from
volcanic vents proves that even Il
very moderate depths there exist sub
stances differing greatly IN deHsity.
a we'll a. IN chemical composition
The lightest lavas are more than twice,
and the heaviest mere than three
times, abe weight Of water. And
materials Of greater density have been
elected by volcanic action. In seek
ing, therefore, TO account for the fact
these dense materials were elected
from the earth's interior in a more or
less molten condition, a simple expla-
nation was otforeded by the suppose
ton that cur planet consisted Of
fluid central mass Enclosed in solid
shell or crust. This shell or crust
was. in proportion to the mass Of the
earth, regarded as but thin firn OF
hardened material. through which the
molten internal matter, from the ex-
pansion due TO heat, or the distur-
Dances occasioned by local dlsnlace-
ments. occasionally forced an opening,
pouring itself forth in streams of red
hot lava. and exhibiting all the other
manifestations of volcanic action.
But geologisis and astronomers have been
led, as the result OF IA more careful and crit
ical examination of the question, TO doubt
the hypothesis that the earth consists of a
great fiuid mass surrounded by compare
lively thin she'll of solid materials. The
general stability of tae earth's crust seems
Ia them to be irTeconcilabie with the sup
Position that If no great depth from -
Surface, the whole mass Of the globe is in q
liquid condition. And if, Is against this OBJ
lection, it he supposed that the solid crust
OF the globe Is several hundreds Of miles in
thickness, il l. difficult. Professor Judd ar
CUES, "a understand how the local centres II
volcanic activity could be supplied from
such decp-scatcd sources. Then again, If
all igneous products were derived from one
central reservoir we might fairly expect io
tind much greater uniformity Of character
among those products than really exists.
In some cases, indeed, materials Of a totally
different composition are elected at the
same time from closely adj lining volcanic
districts. Whatever" he goes on 10 saw,
may be the cause nf volcanic action il
seems clear that II does not originate in a
universal mass al liqueiied material situated
at no great depth from the earth'S surface"
Il Is now very generally admitted, both by
astronomers ana ply icists that il the earth
were not Il rigid mass, its behaviour under
the attractive influences of the surrounding
members ri the solar system would he very
different from what j. found Ia be the case,
and the necessary rigidity would not b; OBJ
tanned were the greater mass Of the earth
tiuId. . hat the GARTH continues Judd.
lis in solid condition 10 a great Lepth from
Tie surface, and possibly quite To The centre,
i "a conclusion concerning which there can
be little doubt"
Seeing. therefore, that this hypothesis sells
aside the central subterranean fluidity from
which all Volcanic action was supposed tn
have cmanated, an explanation OF the phc-
numcna of volcanoes and earthquakes must
bc sought in directions consistent with this
theory OF the clrth's solidity. IL j. impOs-
>Ibic e. give in the space nj command NOR,
than brief note Of The conclusions thai
have been arrived at in the attempt L. sctll,
this question. The first branch Of thu by
pntheSiS advanced Is, that the increase ~
heat with the depth does not extend To- the
whole mass ri the earth that some parts al
the earth interior are of very different
temperature from Others: and that there are
known t. exist such chemical and nccLar-
lcal agencies rs are capable al producing
high temperatures within the crust 81 the
globe. The presence If water. aud III other
liquid and gaseous substances in a state
of ever recurring udmiNtUre with the fused
rock masses. consequent uppu these hlgh
temperatures, j. believed L. Ia the main
cause Of the violent displays # energy cx-
hIbited at volcanic centres. "iolcanors are
usually situated near Csast-lincs, and IL we
imagine iiSSureS u be produced hy which
Sca-waier ilndS access = masses If mean
descent rnCk-matrrialS, then W can regard
volcanic oathulstS Is resulting from this
meeting II water with r'ck-m.-.,, IN d high
~ heated condition"
There l.. r. may he expected from this
hypothesis oi the existence 81 l,,lcs II vary
Ing temperature nj u moderate. ,l.p;h bclnw
the surface, an intimate connection between
the phenomena ri volcanoes and these al
earthquakes. Earthquakes undoubtedly &C.
eur occasionally in districts tn are not now
the scene oi volcanic action; hut if j. uona.
the less certain that earthquakes ~ n rule
take place III those ares which arr the
seats ofv"lCanic action. and that great Garth
quake shocks rreccde and accompany VOL
canlc uuihurSiS. Sometimes -, il has
been noticed that the manifestation 81 az
tlrity at Il volcanic centre i marked 10y the
sudden decline OF the car;huu:.k, ircnors 81
the district around, ~ Though a Sai,-ty-yalyc
had been Opened AT that part OF tine carth's
surface"
The powerful vibrations aud tr,mors of
the ground ion,!ih our feet, which ", call
an earthquake, may therefore ~ nothing
more than the effects Of the contact II
water, as we'll a. ot certain gaseous bodies,
with The ino aEdCScnt rIckS which form these
strata or bands "f high teinpyraiurc; and
the shocks " hiCh follows MAY h, due to the
expanded abb aH.a4suuiSiI. clements thuS
brought together forcing Tor themselves =
vent or passage through the les splil ui
l''Ns resisting 81 tie surrounding ar superb
EumbrEt strata. When the IN .ti..r thus Il. o.
Grated iIna> its way T. ih~ surface. AMI H.
charges HSeiI through tue ii-sar, which Il
has made IN the cartl. We cal; that which
would Otherwise have att, tai is as Al,
earthquake, volcano: - that thv.ss, two 70
MAI kabic maniI,s,; .ti.uS IF power il, nature
ms! M said "a b. twin force, IN, !r,.ti,;s,i
alike - are aHi wafer under COMPRESSION 9.
the one force operating usi.f1rut,;d. and
making the foundations q! In, earth Il shaks.
AZ" "tii"Ic: thc Other force bursting "a way
i"r Ilselt in the surface through the incIn5
lns barriers ~ rCk, and scattering ,icstFgr-
iila ar)uud T.
That this theory Of earthquake shocks
ami volcanic uUgburSiS i consistent with 49,.
cnghate hypothesis II 4 sliid snd not 4 ,lnid
sl"ee, does not appear 10 admit or much
doubt; Sad Il n.as esCa u. al ale..rs. x
satisfaction u timid folks II know thai they
d. not, rs hitherto supposed. islg IN " hat i
merely thin cooled cGus; over mass Of
molten tre, bat on a solid boiy, stnnn- AMI
siEii in al Us parts.